Shortstopping vinyl chloride polymerizations with conjugated dienes



Patented Nov. 4, 1952 SHORTSTOPPIhI G VINYL CHLORIDE POLY- MERIZATIONS' WITH C ON J UGA T E D DIENES Leonard F. Marcus, Waterbury, Conn., assignor to United States'Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. 1 Application July 10, 1951, V

' Serial No. 236,071

'11 Claims. (Cl.'260 92.8)

' This invention relates to improvements in vinyl chloride polymerizations.

The polymerization of liquefied vinyl chloride is generally carried out at mildly elevated temperatures, about 40 C. to 60 C., in an aqueous medium under a pressure'substantially equal to its saturated vapor pressura i; e. about 4to 9 atmospheres, in the presence of a polymerization catalyst. Pressures referred to herein are absolute pressures. The polymerization is generally carried to range of about 60% to 95% conversion of monomer to polymerl All percentagesand parts referred to herein are by weight. The polymerization as is well known may be an emulsion polymerization (see Mark et a1. U. S. Patent 2,068,424, and German Plastics Practice by De Bell, Goggin, and Gloor, pub. by De Belland Richardson, Springfield, Mass, 1946, pages 57-66), or a gr'anular' polymerization (see Lightfoot U. S. Patent 2,511,593, and German Plastics Practice, pages 66-73, and the article'b'y Ruebensaal on Vinyl Resins in Chemical Engineering for December 1950, vol. 57, pages 102 to 105). After conversion of the desired amount of monomer to polymer, residual unreacted monomeric vinyl chloride is removed and the polyvinyl chloride collected by various means, such as by coagulation or spraydryin'g in the case of aqueousemulsion polymerization, or by filtration in the case of aqueous granular polymerization. The resulting polyvinyl chloride is usually washed with water and dried. If the polymerization goes beyond the desired conversion, a polymer having properties inferior to those desired in the final product may'result, particularly as regards I heat and light stability. To avoid this, the batch is generally cooled after the desired conversion;

Undesirable post-polymerization may also take place in the-blow-down tank or in the stripper where unreactedvinylchloride monomer is removed. At the end' of the polymerization, it may be necessary to store or hold the polymer batch for some time without cooling before removing unreacted vinylchloride monomer, In this case the polymerization may continue during storage and thus give a product 01? too high conversion and of resultant undesirable properties. Also,

when the unreacted lvinyl chloride. monomer is' removed from the aqueous medium, there maybe somevinyl chloride monomer, adsorbed on the polyvinyl chloride particles in the aqueous medium, which is not removed until drying of the polyvinyl chloride. monomer may polymerize on the polyvinyl chlorideparticles before it can be removed, adversely afiecting the properties of the finally recovered polyvinyl chloride. It is therefore desirable to add a material which acts to terminate or shortstop the vinyl chloride polymerization reaction after the desired partial conversion of polymerizable monomer to polymer has taken place and to prevent any further polymerization of the residual unreacted vinyl chloride monomer.

I have found that conjugated dienes are efi'ective shortstopping agents for vinyl chloride polymerizations. I

In carrying out thep'resent invention, the conjugatecl diene is added to the polymerization reaction after partial conversion of polymerizable monomer to polymer (usually after about 60% to 95% conversion) and .thereafter the'unreacted vinyl chloride polymer is removed from the aqueous medium, and the polyvinyl chloride recovered in the usual manner. Examples of conjugated dienes that may be used are conjugated diole- I fine hydrocarbons, e. g. butadiene-1,3, isoprene based on the original vinyl chloride monomer used. For practical purposes, the amount of shortstopper may be between 0.02% and 1% by weight of the original vinyl chloride monomer used.

The polymerization reaction is carried out in the presence of a conventional free radicaltype polymerization initiaton'such as a peroxygen 'or' azo catalyst. Examples of peroxygen catalysts are inorganic peroxides, e. g. hydrogenperoiddeand persalts, such as alkali persulfates, alkali perborates, alkali percarbonates';.:and organic "peroxides, e. g., diacetylperoxide, dibenzoyl'peroxide, acetyl benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide,. tertiary butyl hydroperoxide.

This adsorbed vinyl chloride" Examples of azo catalysts are alpha, alpha-abisisobutyronitrile, and p-methoxybenzene diazo thio-2-naphthy1 ether. Catalytic amounts from 0.05% to 2% based on the vinyl chloride monomer may be used.

Tests showing the effectiveness of the chemicals of the present invention as shortstopping agents for vinyl chloride polymerization were carried out according to the following procedure: Into each of a number of crown capped bottles equipped with self-sealing liners was placed a typical granular polymerization recipe using a water-soluble catalyst (100 parts of liquefied vinyl chloride, 320 parts of water, 0.3 part of potassium persulfate and small amounts of buffering and wettin agents). Polymerizations were carried out at 46.6 C. With each shortstopping test, two polymerizations served as controls to show the conversions at an intermediate polymerizationlabout six hours) and at a final polymerization (eight to ten hours) without shortstopping agent. At the end of the intermediate and final polymerization times, monomeric vinyl chloride was immediately vented and percent conversions were obtained. In the test polymerizations, different amounts (based on-100 parts of vinyl chloride monomer used) of a s'hortstopping agent according to the present invention were added to separate polymerization bottles at the same time as the intermediate control polymerizations and the heating was continued to the same overall time as the final control polymerization. Vinyl chloride noonomer was then vented, and percent conversions were obtained by weighing the polymer.

The percent conversions of monomer to polymer of the control after the intermediate and final polymerization times, and the percent c'onversions at the final polymerization times-where the shortstoppers of the present invention were added at the intermediate conversion times, are shown in the following table:

Conversion (percent) Shortstopper added at intermediate conversion Intermediate Final None (final control) 0.1 partjl-vinyl cyclohexene. 0.3 partl-vinyl cyclohexene. 0.5 partl-vinyl cy'clohexene';

Bottle polymerizations similar to the above were-runat 52 C. witha typical granular polymerization recipe using a monomer-soluble catalyst (100 parts of liquified vinyl chloride, 300 parts of water, 0.5 part of lauroyl peroxide and a small amount of suspending agent). Intermediate polymerization times were five and one-half to Six and one-half hours and final polymerization times were eight to ten and one- Series H:

4 half hours. Results are shown in the following table Conversion (percent) Series F:

None (intermediate control) None (final control) 0.02 part isoprene.

0.3 part isop'rena.

None (intermediate control) None (final control) 0.1 part vinyl cyclohexene. 0.3 parts vinyl cyclohexene 0.6 part vinyl cyclohexene The above work shows that the conjugated dienes of the present invention are effective shortstopping agents for vinyl chloride granular polymerizations (the experimental error in the work may be five percent). The chemicals of the present invention are also eiiective as shortstoppers for bulk or mass "oil-phase vinyl chloride polymerizations, and for aqueous emulsion polymerizations which may use inorganic watersoluble catalysts or organic monomer-soluble catalysts. In fact, granular polymerizations which use a monomer-soluble catalyst are generally considered to be mass polymerizations of the individual liquid "monomer globules. In aqueous emulsion and granular polymerizations, the polymerization reaction is generally stopped at 60% to conversion of .monomer to polymer. In bulk polymerizations, the polymerization reaction is generally stopped at lower conversions, e. g., around 40%. With the-shortstopping agents of thepresent invention, the'polymerization reaction may be stopped at any desired conversion.

In emulsion 'polymerizations, it is a simple matter to withdraw a sample 'from the reaction chamber from time to time and to analyze it for total solids in order to determine the percent conversion. O'n'theother'hand. it is almost impossible -to follow the conversion in a granular polymerization by sampling,b'ecause the polymer formed separates so rapidly that a representative sample'cannot be obtained. Thus other methods of determining the amount of conversion, and thereby the point at which the reaction should be stopped, must be used "following polyvinyl chloride ranular polymeriz'ations. For example, the heat evolved in'the' reaction mixture can be measured and be directly correlated with 'the'extent of conversion via thekn'own heat of reaction. Also experience has shown thatpolyvinyl chlorideof {good physical characteristics may be obtained 'by sto ping the reaction at the pressure drop which is at thepoint where the liquid vinylehloride monomer disappears (see German Plastics Practice, pages 61 and 77). In systems where the temperature in the reactor is automatically maintained by regulation of the jacket temperature, the pressure dropwill "be evidenced by a sudden 'pressure" fall. In systems where the pressure in the reactor is automatically maintained by regulation of-the jacket temperatu're-the pressure drop will be evidencedby a rapid-rise in jacket water temperature, whereupon the system is thrown out of automatic control and cooling water is introduced into the jacketresulting in the usual fall of pressure in the reactor. Such methods other than sample analyses of determining Whento shortstop the reaction at the desired conversion may be used in emulsion polymerization as. well as in granu-' lar polymerization. Theevolution ofheat or the viscosity characteristics may be followed in mass.

polymerization to determine the point at which the shortstopping agent shouldv be added.

Thefollowing illustrates the use of the shorti-- stoppers of the present invention in batch aqueous vinyl chloride 'polymerizations. A typical emulsionpolymerization recipe which uses a water-soluble catalyst (100 parts of liquefied vinyl chloridef200 parts oi -water, 0.2 part of potassium persulfate and 1.5 parts of surface-active the desired reaction temperature between 40 C.

and 60 C. and maintained at the desired temperature during the polymerization. The pressure in thereactor at such temperatures will be from4 to 9 atmospheres until theliquid vinyl chlorideis polymerized and the pressuredrops. After the pressure starts to drop and before it drops2atmospheres, 0.02 to 1 part of butadiene- 1,3, isoprene, chloroprene, 2,3-dimethyl butadiene-l,3, piperylene, cyclopentadiene, or l-vinyl cyclohexene, per 100 parts of original vinyl chloride used is added'so that undesirable further polymerization is prevented. Alternatively, the shortstoppin agent may be added at any desired conversion at the discretion of the operator. When the desired conversion has been reached and the shortstop added, the batch may be transferred to the blow-down or storage tank, held there any desired length of time, and then transferred to the stripper when desired for removal of residual unreacted vinyl chloride monomer. Finishing operations after residual monomer removal are conventional as described in the literature references referred to above. The shortstopping agents of the present invention give a greater uniformity of polymer properties, and also result in polymers having enhanced heat and light stability.

The shortstoppers of the present invention ar applicable to shortstopping of modified vinyl chloride polymers which are made by copolymerizing a major proportion, generally over 80% of vinyl chloride and up to 20% of other monoolefinic material which is copolymerizable with yinyl chloride, such as a vinyl alkanoate, e. g.

6 chloride copolymer being made (see .German Plastics Practice," pages 76-78). The same amount of shortstopping agent based on the amount of vinyl chloride employed may be added.

after partial conversion, generally at about 60% to 95% conversion of polymerizable monomeric material to polymeric material. a i

In view of the many changes and modifications that may be made without departing from the principles underlyin the invention, reference should be made to the appended claims .ioran understanding of the scope of the protection afforded the invention.

Having thus described my invention, whatI claim and desire to protect by Letters Patent is:

1; In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride With upto 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of conjug-ated dieneselected from the group consisting of conjugated diolefine hydrocarbons and chloroprene to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

2. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of chloroprene to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

3. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by Weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of butadiene-l,3 to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

4. In the process of preparing a vinyl chloride polymer by the polymerization of material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other monoolefinic material which is copolymerizable with vinyl chloride, the step comprising adding a small amount of isoprene to the reaction mixture during polymerization to stop the same after partial conversion of polymerizable monomeric material to polymeric material.

5. In the process of preparing polyvinyl chloride by the polymerization of vinyl chloride in an aqueous medium, the step comprising adding 0.02% to 1% of conjugated diene selected from the group consisting of conjugated diolefine hydrocarbons and chloroprene based on the weight of the original monomeric vinyl chloride used to the reaction mixture during polymerization to stop the same after about 60% to conversion of vinyl chloride monomer to polyvinyl chloride.

6. The method of preparing a vinyl chloride polymer which comprises subjecting material of the group consisting of vinyl chloride and mixtures of vinyl chloride with up to 20% by weight of the vinyl chloride of other m'onoolefinic material which is copolymerizable with vinyl chloride to polymerizing conditions in an aqueous medium in the presence of a polymerization cata lyst, and after about 60% to 90% conversion of polymerizable monomeric material to polymeric material adding to the polymerization reaction 0.06% to 1% based on the weight of the original monomeric vinyl chloride used. of conjugated diene selected from the group consisting of conjugated diolefine hydrocarbons and chloroprene to stop polymerization of 'unreacted polymerizable monomeric material, and thereafter removing unreacted polymerizable monomeric material from the aqueous medium.

'7. The method of' preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in an aqueous medium in the presence of aper'oxygen catalyst, and after partial conversion of vinyl chloride monomer to polyvinyl chloride adding to the polymerization reaction a small amount of conjugated diene selected from the group consisting. of conjugated diolefine hydrocarbons and chloroprene to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

8. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of conjugated diene selected from the group consisting of conjugated diolefine hydrocarbons and chloroprene to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

9. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in thepresence of a peroxygen catalyst in an aqueous medium at a temperature between 40 C. and C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of chloroprene' to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

10. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizing conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 40 Cpand 60 C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop .and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of butadiene-l,3 to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

11. The method of preparing polyvinyl chloride which comprises subjecting vinyl chloride to polymerizin conditions in a closed vessel in the presence of a peroxygen catalyst in an aqueous medium at a temperature between 40 C. and 60 C. under a pressure substantially equal to its saturated vapor pressure of about 4 to 9 atmospheres, and after the pressure begins to drop and before it has dropped 2 atmospheres adding to the polymerization reaction a small amount of isoprene to stop polymerization of unreacted vinyl chloride monomer, and thereafter removing unreacted vinyl chloride from the aqueous medium.

LEONARD F. MAROUS.

No references cited. 

1. IN THE PROCESS OF PREPARING A VINYL CHLORIDE POLYMER BY THE POLYMERIZATION OF MATERIAL OF THE GROUP CONSISTING VINYL CHLORIDE AND MIXTURES OF VINYL CHLORIDE WITH UP TO 20% BY WEIGHT OF THE VINYL CHLORIDE OF OTHER MONOOLEFINIC MATERIAL WHICH IS COPOLYMERIZABLE WITH VINYL CHLORIDE, THE STEP COMPRISING ADDING A SMALL AMOUNT OF CONJUGATED DIENE SELECTED FROM THE GROUP CONSISTING OF CONJUGATED DIOLEFINE HYDROCARBONS AND CHLOROPRENE TO THE REACTION MIXTURE DURING POLYMERIZATION TO STOP THE SAME AFTER PARTIAL CONVERSION OF POLYMERIZABLE MONOMERIC MATERIAL TO POLYMERIC MATERIAL. 